The goal of the proposed project is to test the hypothesis that core metabolism of the medically important cavity parasites of humans, the amitochondriate Giardia lamblia, Entamoeba histolytica and Trichomonas vaginalis differs markedly from that of their human host. It will also be explored to what extent the unique and diverse "chimeric" metabolic patterns of these organisms are due to evolutionary losses or new acquisitions of enzymes. In the next grant period emphasis will be placed on two critical but essentially unexplored aspects of "amitochondriate" parasites, a) carbohydrate (glycogen) reserves and their regulation and, b) enzymes involved in electron transport, to complement accumulating data on glycolysis and its distal extensions. a) Enzymes involved in the mobilization of glucose from glycogen and of glycogen synthesis will be expressed in heterologous systems, purified and studied with biochemical methods, with special emphasis on their regulatory properties. In addition, both the sequences and physiological characteristics of the enzymes will be evaluated in comparison with existing data in order to obtain insight into their evolutionary relationships. b ) Enzymes transferring reducing equivalents from glycolytically reduced NADH and ferredoxin to diverse electron acceptors and O2 will be explored with essentially the same approaches.